This invention is of important beneficial effect to the environment and relates primarily to apparatus for detecting the presence of hydrocarbons in underground aquifer formations and for the removal of such hydrocarbons.
The convenience of modern-day life in America, with the proliferation of personal automobiles available to almost everyone, has not been achieved without cost. Accompanying the ubiquitousness of the automobile has been the development of a huge infrastructure to attend to the specialized needs of the automobile and the motoring public. This infrastructure--which comprises a significant portion of our gross national product--has produced fuel dispensing stations at almost every significant intersection and an entire industry to find, produce, refine, transport and store the hydrocarbon products which drive the industry. Unfortunately, as the industry has continued to expand and to accord even greater convenience to the public, the number of possible point sources of pollution has increased also.
These possible point sources of pollution are as varied as the industry, varying from individual service stations with leaking underground tanks and intermittant spillages from normal operations to large fuel depots, pipelines, pumping stations, refineries and other processing plants. In many cases, the pollution was eliminated at the source years ago, but even those former sources of pollution present a continuing hazard to the environment as the spilled hydrocarbons continue to work their way down through surface layers of soil into the aquifers below. Since a very small amount of such products can contaminate a large amount of ground water--it is estimated that less than one ounce of gasoline is sufficient to render a hundred thousand gallons of water unsafe for human consumption, for example--it is apparent that a considerable need exists for an accurate, economical and rapid means of monitoring the pollution rate of underground aquifers and for retrieving the pollutants once detected.
Most of the nation's two hundred thousand plus service stations are required to have what is known as monitoring wells near their possible sources of pollution. These typically are small-diameter wells which extend from an accessible surface location down to the water formation below. Various types of instruments are then lowered into the wells to detect the presence of polluting hydrocarbons, but most of such instruments are one of two general types, either of fixed flotation design or free floating.
Both designs typically comprise long thin cylinders with a perforation arrangement of some sort to allow the contaminants on the surface of the water to enter the cylinder. With the fixed flotation design, the instrument as a whole is intended to remain suspended at a constant height regardless of variations in water height. Typically in this class, the design is such as to permit an internal product collection head to float up or down within the fixed cylinder as the water level varies. Naturally, the maximum length of travel possible within a collection device of this type is limited by the length of the cylinder between the collection chamber and the head of the device which, under the best of conditions, may be as little as two feet. In use, however, the device is initially positioned in a well such that its floating product collection head may either rise or sink as the water level in the well rises or sinks. Thus, if the water level in a monitoring well employing a device of this type should drop by more than one foot, the level of pollutants on the surface of the water would be below the range permitting intake of the pollutants, and the device would simply cease to function. Similarly, should the water level rise by more than one foot, the pollutant level would be above the level which permits intake, and the device similarly would cease to function.
In practice, however, the real limits on permissable travel are even less than the design limits described above. All devices of this type known to applicant incorporate a coil of flexible tubing communicating between the floating collection head and the product collection chamber below which transmits the captured pollutants from the head to the collection chamber. All such coils to some extent function physically like a spring; they have a certain resistance to being extended, and to being compressed. In practice, as the water level drops, the weight of the floating product collection head interior to the device may not be sufficient to fully compress a tubing coil which may have taken a "set" at an extended position, and, therefore, the device may cease functioning with a drop in water level of even less than the design limit of one foot. Similarly, a tubing coil which has long been fully compressed before placement in a well may have a resistance to full extension greater than the slight upward force on the floating collection head provided by its force of buoyancy, and may thus similarly not be able to extend to its full design limit with a rise in the water level of the well. Further, such coils weaken and deteriorate with age, and frequently break, thereby transmitting the pollutants taken in by the floating head not to the collection chamber but only to that portion of the device between such chamber and the floating collection head. Since this portion of the device is in open communication with the surrounding well water, however, the pollutants taken in by the collection head are readily dispersed back to the well.
Still another defect, and an important one, in many such devices arsies from their designed dependence upon their ability to precisely position the floating collection head with regard to the water/pollutant level. This is to say that many devices of this type are not capable of excluding water from the collection head if the water level rises above the designed "float point" of the collection head. Not only will devices of this type cease functioning when the water level rises beyond the maximum permitted travel, but such devices will actually permit water to be taken in under these circumstances and displace previously collected pollutants from the collection chamber. Under such circumstances, then, such devices fail to serve any purpose whatsoever. Not only do they fail to collect any pollutants, but by giving a false indication of no pollutants could actually disguise the presence of severe pollution for an extended period of time with harmful consequences for the environment. Additionally, such devices require vent tubes to allow free movement of the floating collection head; when these tubes are not properly installed, as is often the case, water may enter through such tubes and drive out collected hydrocarbons.
The other general type of passive monitoring/recovery devices has its own set of limitations. In general, devices of this class are intended to float up and down in their entirety, rather than just one part within such devices. Devices of this class generally have a cylindrical recovery chamber surmounted by a fixed hydrocarbon/water separator fully exposed to its surroundings. A safety chain is normally attached to the top of the separator which both limits the downward permitted travel of the device and permits recovery from the well when desired.
Devices of this sort may have a permitted range of travel considerably greater than devices of the first type. These devices will continue to function so long as the water/pollutant interface is anywhere along the working length of the separator. However, travel distance is achieved by continuing to pay out free length of chain into the well after the device has reached its floation level. Since chains are notoriously not buoyant, the freedom to travel downward--which is achieved only by the additional lengths of chain beyond the buoyant point--imposes a considerable limit on the freedom to travel upwards. The extra lengths of chain may be thought of as a loop of chain from the top of the device down to the bottom of the loop and then back up to the surface, a portion of which tends to weight down the device. Thus the amount of surplus chain that initially can be provided is limited to that which would weight down the separator below the water level. However, not even that amount can actually be used since no upward movement at all would be achieved: a rising water level would result in even more slack chain and even more weight to drag down the floating device. Thus in practice such devices are actually able to achieve little more than 2 or 3 feet of vertical movement from an initial floating position. Since a large number of monitoring wells are shallow, their water levels can and do change considerably, with the result that such travel limitations are significant in their effect on the operational useful of such devices and on the environment.
The hydrocarbon/water separators of most such devices typically comprise a perforated polyvinylchloride tube with an inner filter normally consisting of a hydrophobic membrane and an outer filter consisting of a hydrocarbon-attractive media. Such filters are normally glued securely to the polyvinylchloride tube to insure that no water seeps into the tube around the edges of the filters. However, the hydrocarbon base of such glues tends to leach out into the well water, thereby giving false indications of pollutants even when no pollutants are present. Such false positives can cause remedial actions and their attendant costs in both time and money to be incurred needlessly.
In addition, the typical prior art collection/monitoring device utilizes a ball or other valve at the bottom of the collection chamber for emptying the collected pollutants at the surface for proper disposal. Since a filled or nearly-filled device is both heavy and wet, and often has an oily film thereon as well, it is frequently dropped when not intended and the collected pollutants are often accidently discharged at the surface, thereby starting the pollution cycle over from the beginning.